Repeater connection



i Dec. 7 1926.

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Inventor: Walther* \^/0|ff,

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Patented Dec. 7, V1926.

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WALTHER WOLFF, OF BERLIN-NIEDERSCHONVJEDE, GERMANY, .ASSIGNOR TO GEN- ERAL ELECTRIC COMPANY, A CORPORATION 0F NEW YORK. l

RETEEATER CONNECTION.

Application filed July 13, 1923, Serial No. 651,412, and in Germany September 15. 1922.

My present invention relates to improvements in connections which may be employ-ed for repeaters or amplifiers connecting two sections of a speech transmission system.

The object of my invention and the novel features thereof will best be understood by reference to the following description taken in connection with the accompanying drawing in which Fig. 1 is a diagrammatic representation of' a portion of a transmission system in which my invention is incorporated and Fig. 2 shows some characteristic curves illustrating the advantages which may be obtained by the use of my invention.

It is known that the impe-dances of transmission lines that are connected together through amplifying repeaters must either be equal or must be capable of being simulated by artificial lines. For the latter purpose means are disclosed in U. S. Patent 1,167,693, of R. S. Hoyt, and by K. Kupfmller in German Patent 330,964. The arrangements Chown in these patents however are limited to the reproducing of the theoretically calculated impedance.' As a matter of fact, however, theimpedance of a line for the various frequencies usually shows very great deviation from'the calculated mean values, which deviation may amount to and more. It is clear that in such cases, with an exact simulation of the theoretical mean value of the impedance of' the line, little is accomplished. Measurements show that the percentage of variations is substantially reduced if at the end of the line between the conductors a, and shown in Fig. 1, large condenser C is connected of the order of magnitude of .07 F. to .15 F.,- or even larger. The impedance of the line, thus smoothed out, may then, in well known manner, be conveniently and easily simulated by means of combinations of suitable resistances, condensers or th-e like, as conventionally indicated at N in Fig. 1. The condenser C however acts, for the higher frequencies, like a low impedance shunt, A considerable portion of the high frequency energy therefore flows through it and does not arrive at the amplifier A of' the repeat-er circuit V, Fig. 1. Consequently the higher frequencies are more strongly attenuated than the lower frequencies, so that speech is much distorted.

The object of the invention is a device by means of which this distortion is equalized to such an extent that thc residual distortion is practically harmless for the operation of the line. This is made possible by means of a method of construction of the amplifier which has a specially selective action. To this end the amplifier is given an amplification curve which rises for the rango of frequency from 6,000 to 10.000. l.Vithin this range therefore, for which the condenser causes a greater attenuation by reason of its properties, a greater amplifying action will be obtained. It will, of course, be understood that the methods for modifying the action of an amplifier in the manner described are well known in the art.

These conditions are shown diagrammatically in Fig. 2. The interval ab represents that range of the audio frequencies within which, by reason of the condenser action, an approximate constancy in the attenuation of the frequencies exists, provided a non-Selective amplifier is employed. The high frequencies in the part bc ofthe curve. which are essential forV the reproduction of speech, have accordingly too great attenuation. If now the amplifier is so constructed that it has a particularly select-ive action for just this range as indicated by the curve be, then the total range of audio-frequencies will be in accordance with the curve afl, and speech will be transmitted without perceptible distortion. This action of an ampliiier possessing a high counter distorting effect is all the more valuable in that it can be graduated according to the character and the length of the line, by the connection and disconnection of capacities, without loss of advantage as regards the reproducing effect. By the combination of a variable shunt condenser with an amplifier of the kind mentioned there-fore a system is provided which has a number of technical advantages. The advantage consists in the fact that, first, by reason of the large variable condenser, the impedance of the long-distance line is smoothed out, and thereby the simulation of the impedance of the longdistance line is substantially facilitated, and that, second, by the choice of high counter distortion for the amplifier, the quality of the amplified speech does not. suffer. A further advantage consists in the fact that vexact equality between the counter distortion of the amplifier and the distortion of the long-distance line or the cable is no longer important. On the contrary, the amplifier is giiv'en at the beginning a high counter distortion, which then is eqi'ia'l'ized by the large variable condenser without the necessity for the counter distortion o'f the ampiier to be exactly adapted to the existing conditions ol the line .in question, while heretofore. in the case of vamplifiers possessing only slight counter distortion, care has had to be taken that the speech should be undistorted by just as much as it *as distorted by the cable leadingr to the amplifier.

lVhat I claim as new and desire to secure by Letters Patent ot' the United States, is:-

1. The combination in a repeater system of a transmission line which is sliunted by a capa-city of such Value as to offer comparatively 10W impedance for the higher voice frequencies, means t0 sil'nulate the impedance oi the line as thus modified, and an ampliiier connected to said line which produces a greater ampliiication of the higher Voice frequencies than of the lower.

2. The combination ,in a repeater systen'i ot' a transmission line. which is shunted by a \i"ariab'1e capacity ot'. such Values as to ofter comparatively low impedance to the higher yoice frequencies whereby the variation ot the impedance oi the line with variations in the frequency of th'e current transmitted is greatly decreased, means to simulate the impedance o'f the line as thus modified, and an amplifier connected to said line which is adjusted to counteract the. distortion in transmission produced by the shunt capacity.

In witness whereof, have hereunto set my hand this 14th day ot June 1923.

Dn. W'ALTHER WOLFF. 

